Ride height

[tom whitton1]

As someone mentioned, I use a length of 4x4 as a ride height gauge.
Overall, the block 9-3/4" high. One half of the block is cut down to
8-7/16" high. The high part is labelled "Front", the lower, "Rear". Those
are the heights of the bottom of the frame directly below the front and
rear measurement ovals when the ride height is correct. (Fact is, I thing
the 8-7/16" is 1/16" in error).

But what I really want to get across is that, despite its importance to
proper handling, we need to realize just what the effect of ride height is
on caster change. Remember that the wheelbase of a 26' GMC is 160". From
simple trigonometry, a 1" change in front vs rear ride height will yield
only 0.358* of caster change (arctan (1/160)). So, to achieve 1* more
caster, we'd have to ride around with the rear airbags almost all the way
down (it rides hard there).

Ken H.

 

[kab7]

> A pic of the "upper control arm rear adjuster" adjusted to it's maximum caster position might help.

http://www.machinesoflovinggrace.net/gmc/frontend/Images/Picture%20292-trim.jpg

Karen
1975 26'

 

[jim kanomata1]

Jim H,
Your correct as when I was Zone svc rep for Ford Motor co, we were running
into that type or harmonic vibration and the fix for it was you say.

> > A pic of the "upper control arm rear adjuster" adjusted to it's maximum
> caster position might help.
>
>
> http://www.machinesoflovinggrace.net/gmc/frontend/Images/Picture%20292-
> trim.jpg
>
> Karen
> 1975 26'
>
>
>
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--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk
http://www.appliedgmc.com
1-800-752-7502

 

[brian waddell]

I believe you guys are mixing up caster and camber....brian 77 ele455

________________________________
From: Gmclist on behalf of A.
Sent: September 8, 2016 12:22 PM
To: gmclist
Subject: Re: [GMCnet] Ride height

> Ken,
> Man I never realized how much a change of camber of 0.358 degrees could make! WOW - NOT!
>
>
>
> Maybe you have put this GMC myth to bed!
>
> Regards,
> Rob M.
> USAussie - Downunder
> AUS '75 Avion - The Blue Streak TZE365V100428
> USA '75 Avion - Double Trouble TZE365V100426
I believe Ken is probably right about the caster not being significantly affected by ride height settings, and not contributing to handling issues.
But there is also probably a valid reason that the GM engineers spec'd the front to be an inch and a half higher than the rear. It might be that
somehow it affects the airflow and that's what makes the steering squirrely when that difference is not right. I dunno.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."

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[a.]

> I believe you guys are mixing up caster and camber....brian 77 ele455
> From: Gmclist on behalf of A. Sent: September 8, 2016 12:22 PM To: gmclist
> Subject: Re: [GMCnet] Ride height

> > Ken,
> > Man I never realized how much a change of camber of 0.358 degrees could make! WOW - NOT!
> >
> >
> >
> > Maybe you have put this GMC myth to bed!
> >
> > Regards,
> > Rob M.
> > USAussie - Downunder
> > AUS '75 Avion - The Blue Streak TZE365V100428
> > USA '75 Avion - Double Trouble TZE365V100426
> I believe Ken is probably right about the caster not being significantly affected by ride height settings, and not contributing to handling
> issues.
> But there is also probably a valid reason that the GM engineers spec'd the front to be an inch and a half higher than the rear. It might be that
> somehow it affects the airflow and that's what makes the steering squirrely when that difference is not right. I dunno.
> --
> 73 23' Sequoia 4 Sale
> 73 23' CanyonLands Parts Unit 4 Sale
> Upper Alabama
> "Highest price does not guarantee highest quality."
I'm sure Rob meant caster. We understood each other, even if nobody else did.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."

 

[robert mueller]

No we're not.

I was being sarcastic.



Regards,
Rob M.
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426

-----Original Message-----
From: Gmclist [mailto:gmclist-bounces] On Behalf Of Brian Waddell
Sent: Saturday, September 10, 2016 12:20 PM
To: gmclist
Subject: Re: [GMCnet] Ride height

I believe you guys are mixing up caster and camber....brian 77 ele455

 

[robert mueller]

Oops - I meant caster!

DOUH!

Regards,
Rob M.
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426

-----Original Message-----
From: Gmclist [mailto:gmclist-bounces] On Behalf Of A.
Sent: Saturday, September 10, 2016 1:06 PM
To: gmclist
Subject: Re: [GMCnet] Ride height

I'm sure Rob meant caster. We understood each other, even if nobody else did.
--

 

[stephen thomas]

So, it seems I'm having a different kind of problem then most. The
adjustments I make on the right side make far less of a change in ride
height than the left. At the moment, the right side adjustment bolt is
turned in about 6 revolutions more than the left and is about 1/2 lower at
12 1/2".

Is it possible to over due it? I'm getting nervous about trying to adjust
the left side up any more.

Steve
78 Eleganza
Santa Cruz, CA

On Sat, Sep 10, 2016 at 12:30 AM, Rob Mueller
wrote:

>
> Oops - I meant caster!
>
> DOUH!
>
> Regards,
> Rob M.
> USAussie - Downunder
> AUS '75 Avion - The Blue Streak TZE365V100428
> USA '75 Avion - Double Trouble TZE365V100426
>
>
> -----Original Message-----
> From: Gmclist [mailto:gmclist-bounces] On Behalf Of A.
> Sent: Saturday, September 10, 2016 1:06 PM
> To: gmclist
> Subject: Re: [GMCnet] Ride height
>
> I'm sure Rob meant caster. We understood each other, even if nobody else
> did.
> --
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[Ken H.]

Stephen,

It sounds to me like you may have a bad weight bias in the rear. If the
Left Rear is heavier than the Right Rear, the Right Front adjustment will
be affected. Accurate weight measurement (and lateral equalization) at all
four corners should be the first step in ride height adjustment.

Ken H.

On Tue, Sep 20, 2016 at 2:48 PM, Stephen Thomas
wrote:

> So, it seems I'm having a different kind of problem then most. The
> adjustments I make on the right side make far less of a change in ride
> height than the left. At the moment, the right side adjustment bolt is
> turned in about 6 revolutions more than the left and is about 1/2 lower at
> 12 1/2".
>
> Is it possible to over due it? I'm getting nervous about trying to adjust
> the left side up any more.
>

 

[RF_Burns]

Steve,
Make sure you have your rear ride height set and then put blocks under the rear bogies and set the weight of the coach on the blocks maintaining the
rear height as close as possible. This prevents a kitty-corner (or is it catty-corner) rocking effect from the upward force of the rear suspension.
Then do your front heights.

Just what this old Ex-Farm boy shade tree mechanic did.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
Hubler 1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

 

[jim kanomata1]

Steve
Your unit must be crooked on that side
Check it

Sent from my iPhone

>
> So, it seems I'm having a different kind of problem then most. The
> adjustments I make on the right side make far less of a change in ride
> height than the left. At the moment, the right side adjustment bolt is
> turned in about 6 revolutions more than the left and is about 1/2 lower at
> 12 1/2".
>
> Is it possible to over due it? I'm getting nervous about trying to adjust
> the left side up any more.
>
> Steve
> 78 Eleganza
> Santa Cruz, CA
>
>
>
> On Sat, Sep 10, 2016 at 12:30 AM, Rob Mueller

>
>>
>> Oops - I meant caster!
>>
>> DOUH!
>>
>> Regards,
>> Rob M.
>> USAussie - Downunder
>> AUS '75 Avion - The Blue Streak TZE365V100428
>> USA '75 Avion - Double Trouble TZE365V100426
>>
>>
>> -----Original Message-----
>> From: Gmclist [mailto:gmclist-bounces] On Behalf Of A.
>> Sent: Saturday, September 10, 2016 1:06 PM
>> To: gmclist
>> Subject: Re: [GMCnet] Ride height
>>
>> I'm sure Rob meant caster. We understood each other, even if nobody else
>> did.
>> --
>>
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

 

[jim kanomata1]

Oh, your addressing the front
Call me and I'll show you how to check it as I think you might have a popes hex in the A frame

Sent from my iPhone

>
> So, it seems I'm having a different kind of problem then most. The
> adjustments I make on the right side make far less of a change in ride
> height than the left. At the moment, the right side adjustment bolt is
> turned in about 6 revolutions more than the left and is about 1/2 lower at
> 12 1/2".
>
> Is it possible to over due it? I'm getting nervous about trying to adjust
> the left side up any more.
>
> Steve
> 78 Eleganza
> Santa Cruz, CA
>
>
>
> On Sat, Sep 10, 2016 at 12:30 AM, Rob Mueller

>
>>
>> Oops - I meant caster!
>>
>> DOUH!
>>
>> Regards,
>> Rob M.
>> USAussie - Downunder
>> AUS '75 Avion - The Blue Streak TZE365V100428
>> USA '75 Avion - Double Trouble TZE365V100426
>>
>>
>> -----Original Message-----
>> From: Gmclist [mailto:gmclist-bounces] On Behalf Of A.
>> Sent: Saturday, September 10, 2016 1:06 PM
>> To: gmclist
>> Subject: Re: [GMCnet] Ride height
>>
>> I'm sure Rob meant caster. We understood each other, even if nobody else
>> did.
>> --
>>
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

 

[stephen thomas]

Ken, Bruce,

I don't have scales readily available, but I'm fairly confident that the
weight in the front and rear is roughly evenly distributed. The generator
has been replaced with storage and the water tank removed and replaced with
2 low profile, smaller tanks, one on either side, closer to the front of
the coach. Everything in the (house) interior, except for the original
bath, was made by me and I've done the best I could, without scales, to
distribute the weight evenly. But again, I've never weighed it, so I don't
know for sure.

I did read through most of this thread before I started trying to adjust
the height, so I am using blocks under the frame at the rear measuring
points.

I should also mention that the torsion bar on the right side was very hard
to get back in. It took two of us to pull it towards the outside of the
coach to get it back in the hole on the cross member (I suspect this is due
to a front end accident on that side). So, I feel like it has a bit of a
bend to it that the other side doesn't. It's hard to tell, though, when
your on your back, underneath looking up. Anyway, this is why I'm worried
about over torquing what may already be a stressed out torsion bar.

Maybe 12 1/2 is high enough and I should lower the left to match?

Thanks,
Steve
78 Eleganza
Santa Cruz, CA

> Steve,
> Make sure you have your rear ride height set and then put blocks under the
> rear bogies and set the weight of the coach on the blocks maintaining the
> rear height as close as possible. This prevents a kitty-corner (or is it
> catty-corner) rocking effect from the upward force of the rear suspension.
> Then do your front heights.
>
> Just what this old Ex-Farm boy shade tree mechanic did.
>
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
> Hubler 1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[charles boyd]

Did you lay the torsion bar on flat concrete to see if it was twisted or bent? The right side does see more abuse and with rears blocked at ride
height and bags dumped you may have to even use a longer adjusting bolt to get to 13.
--
C. Boyd
76 Crestmont
East Tennessee

 

[sgltrac]

Steve,

If you suspect frame twist damage a relatively easy twist check is to
support the frame in three places at two frame main x members. The rear x
member at the bogie pivots would be a good location to support with two
stands (one under each bogie) then another in the center of the front
cradle x member. If you lift the rig gradually until there is little or no
pressure on the tires (don't forget to air down the bags as you un weight
the rear suspension ) and it is supported close to level with the floor in
those three points and the frame is twisted it should become visibly
apparent. I suspect however the torsion bar is bent or lost its spring as
has been mentioned. The twist check would allow you a relatively quick and
painless way to rule out the structure however. After ruling out twist you
can check for diamond or short rail by measuring diagonally from the left
side of a x member to the right of an x member forward or aft of the first.
Should have numbers very close to each other say within 1/4-3/8". Make sure
you are measuring from symmetric points. If you have holes or frame rivet
heads in the bottom of the frame which are easy to access and you can
confirm them as symmetric they should suffice.

Sully
77 eleganza 2
seattle

On Tue, Sep 20, 2016 at 3:04 PM, Charles Boyd
wrote:

> Did you lay the torsion bar on flat concrete to see if it was twisted or
> bent? The right side does see more abuse and with rears blocked at ride
> height and bags dumped you may have to even use a longer adjusting bolt to
> get to 13.
> --
> C. Boyd
> 76 Crestmont
> East Tennessee
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[Ken B]

> Ken, Bruce,
>
> I don't have scales readily available, but I'm fairly confident that the
> weight in the front and rear is roughly evenly distributed. The generator
> has been replaced with storage and the water tank removed and replaced with
> 2 low profile, smaller tanks, one on either side, closer to the front of
> the coach. Everything in the (house) interior, except for the original
> bath, was made by me and I've done the best I could, without scales, to
> distribute the weight evenly. But again, I've never weighed it, so I don't
> know for sure.
>
> ** SNIP **

Even without scales, you can get is much closer than you have it now.

Adjust the rear ride height FIRST. (no scales needed.) Then rest the rear end on blocks of EQUAL heights and somewhere close to the correct ride
height. This will prevent the dynamic effects of the rear system and movement of the airbags while you are adjusting the front. To block the rear
simply cut some adjustment blocks of equal height and put them under the frame or under the center support of the bogies. Then drop the air bag
pressure slightly until the coach is resting on the blocks enough that it can not move. The full weight of the coach on the blocks is not necessary.
Just enough weight to prevent it from moving. We have found an imbalance on the rear heights causes 125 pounds of weight shift for each 1/4".

Now go to the front and adjust the torsion bars for equal ride heights (and weight if you have scales available). We usually do it this way without
scales and then check the weights after we are done.

Usually we find one side is slightly heavier than the other. In that case, on final adjustment with scales, we try to make the front and rear heavy
on the same side. We also try to settle for no more than 100 pounds side to side difference in both the front and rear.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

 

[stephen thomas]

Ken, this is exactly how I've been measuring. I think part of the issue has
been that the old cement pad I'm working on just isn't as even as I
thought, so the block under the frame on the rear right may have been a
little low. The other thing is that I was just too afraid to tighten the
adjustment screw on the right side so far beyond the amount that I had
turned the screw on the left side. A pep talk from Jim K got me over that.

Yesterday, I moved the coach and remeasured, readjusted, drove around for a
while then measured again. I'm still slightly low, but at least it seems to
be even at 12 7/8" on both sides. I need to find a better place to measure.

Thanks
Steve

> > Ken, Bruce,
> >
> > I don't have scales readily available, but I'm fairly confident that the
> > weight in the front and rear is roughly evenly distributed. The generator
> > has been replaced with storage and the water tank removed and replaced
> with
> > 2 low profile, smaller tanks, one on either side, closer to the front of
> > the coach. Everything in the (house) interior, except for the original
> > bath, was made by me and I've done the best I could, without scales, to
> > distribute the weight evenly. But again, I've never weighed it, so I
> don't
> > know for sure.
> >
> > ** SNIP **
>
>
> Even without scales, you can get is much closer than you have it now.
>
> Adjust the rear ride height FIRST. (no scales needed.) Then rest the
> rear end on blocks of EQUAL heights and somewhere close to the correct ride
> height. This will prevent the dynamic effects of the rear system and
> movement of the airbags while you are adjusting the front. To block the
> rear
> simply cut some adjustment blocks of equal height and put them under the
> frame or under the center support of the bogies. Then drop the air bag
> pressure slightly until the coach is resting on the blocks enough that it
> can not move. The full weight of the coach on the blocks is not necessary.
> Just enough weight to prevent it from moving. We have found an imbalance
> on the rear heights causes 125 pounds of weight shift for each 1/4".
>
> Now go to the front and adjust the torsion bars for equal ride heights
> (and weight if you have scales available). We usually do it this way
> without
> scales and then check the weights after we are done.
>
> Usually we find one side is slightly heavier than the other. In that
> case, on final adjustment with scales, we try to make the front and rear
> heavy
> on the same side. We also try to settle for no more than 100 pounds side
> to side difference in both the front and rear.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>